(A) Field of the Invention
The present invention relates to a liquid crystal polymer composition having balanced properties of excellent mechanical characteristics, heat resistance, thin wall moldability, dimensional stability and lubricating property (wear resistance) as well as a property capable of providing molded articles having excellent appearance. More specifically, it relates to a liquid crystal polymer composition capable of forming thin-walled molded articles having improved strength and anisotropy and having a high critical PV value and superior lubricating property (wear resistance) whereby the degree of damage of soft metals such as aluminum alloy becomes extremely low. The present liquid crystal polymer composition is suitable for use in various applications including, for example, electrical parts, electronic and equipment parts, automotive parts, precision machinery parts, audio parts, optical fiber parts, office automation equipment parts and chemical apparatus parts.
(B) Description of the Prior Art
The need for plastic materials having high performance have been growing in recent years. Numerous polymers having various new types of performance have been developed and marketed. However, optical anisotropic liquid crystal polymers characterized by parallel sequences of molecular chains, have been particularly noted due to their superior flowability and mechanical properties. Examples of such polymers capable of forming an anisotropic melt include, for example, a liquid crystal polyester obtained by copolymerizing polyethyleneterephthalate with p-hydroxybenzoic acid (Japanese Unexamined Patent Publication No. 49-72393), a liquid crystal polyester obtained by copolymerizing p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid (Japanese Unexamined Patent Publication No. 54-77691), a liquid crystal polyester obtained by copolymerizing 4,4'-dihydroxybiphenyl, terephthalic acid and isophthalic acid with p-hydroxybenzoic acid (Japanese Examined Patent Publication No. 57-24407), a liquid crystal polyester amide formed from 6-hydroxy-2-naphthoic acid, p-aminophenol and terephthalic acid (Japanese Unexamined Patent Publication No. 57-172921), and a liquid crystal polyesteramide formed from p-hydroxybenzoic acid, 4,4'-dihydroxybiphenyl, terephthalic acid, p-aminobenzoic acid and polyethylene terephthalate (Japanese Unexamined Patent Publication No. 64-33123).
However, it is also well known in the art that these liquid crystal polymers have disadvantages including low mechanical strength in the direction perpendicular to the flow direction and a large molding shrinkage, or in other words, mechanical anisotropy and dimensional anisotropy are extremely large. Although liquid crystal polymers are especially used as thin-walled molded products due to their superior flowability and mechanical properties, there are problems in that the thinner the walls of the molded products, the larger anisotropy becomes. Examples of methods that have been proposed to improve the above-mentioned disadvantages include a method wherein a glass fiber is added to a liquid crystal polymer (Rubber Digest, Vol. 27, No. 8, pp. 7-14, 1975), a method wherein a potassium titanate fiber is blended into a totally aromatic copolyester (Japanese Unexamined Patent Publication No. 61-195156), a method wherein a potassium titanate fiber having no water is blended into a thermotropic liquid crystal polymer (Japanese Unexamined Patent Publication No. 62-81448), and a composite material comprising a thermoplastic synthetic resin and a potassium 6-titanate fiber (Japanese Unexamined Patent Publication No. 1- 301516).
However, in the case of the former attempt, namely, a method involving the addition of a glass fiber, is effective in reducing anisotropy, but the impact strength is decreased, the appearance becomes poor and the flowability is impaired. In addition, in relation to the abrasive wear resistance, although the critical PV value are improved, the damage given to the opposing material becomes conversely large, and therefore, this method has the fatal defect of being extremely difficult to be used practically in applications requiring large abrasive wear resistance. In addition, in the latter method involving the blending of a potassium titanate fiber, although this method is effective to a certain extent in improving the appearance of molded products and improving abrasive wear resistance, these effects are not necessarily sufficient. Thus, since the mechanical performance and the anisotropy of thin-walled molded products are inferior compared to the former method, these methods cannot be used practically. One of the reasons why the mechanical performance is poor is considered to be the result of elution of alkaline components from the potassium titanate during blending of potassium titanate fiber into the polymer at high temperatures (and more remarkable in the case where the potassium titanate fibers are broken). These alkaline components are dissolved in the minute amount of water contained in the polymer, whereby the hydrolysis of the polymer is promoted. It has also been learned that the decrease in mechanical performance is more remarkable especially in the case of the liquid crystal polymer containing ethylenedioxy units as is disclosed in Japanese Unexamined Patent Publication No. 49-72393.